til/ruby/make-structs-easier-to-use-with-keyword-initialization.md

Make Structs Easier To Use With Keyword Initialization

Typically a Struct in Ruby is defined and initialized like so:

> Subscriber = Struct.new(:email, :first_name, :status, :tags)
=> Subscriber
> s1 = Subscriber.new('bob.burgers@example.com', 'Bob', :active, [:food, :family])
=> #<struct Subscriber email="bob.burgers@example.com", first_name="Bob", status=:active, tags=[:food, :family]>
> s1.email
=> "bob.burgers@example.com"

That's a nice way to structure light-weight objects.

A potential challenge with multi-argument Struct definitions like this, especially when they aren't colocated with initialization, is that it can be hard to remember or distinguish the argument order when initializing an instance of one.

Ruby 2.5 added the keyword_init option to help with this exact issue. When that option is set to true for a Struct definition, then we get to initialize it with keyword arguments rather than positional arguments.

> Subscriber = Struct.new(:email, :first_name, :status, :tags, keyword_init: true)
=> Subscriber(keyword_init: true)
* s1 = Subscriber.new(
*   first_name: 'Bob',
*   email: 'bob.burgers@example.com',
*   tags: [:food, :family],
*   status: :active
> )
=> #<struct Subscriber email="bob.burgers@example.com", first_name="Bob", status=:active, tags=[:food, :family]>
> s1.email
=> "bob.burgers@example.com"

Notice I have to use keyword arguments now and that because of that I can organize them in whatever order makes sense. Coming back to view this line of code later, it is easy to see attribute each value corresponds to.

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